public class cirlce {
    double r;
    public void area(){
        double pai = 3.14;
        double s = pai * r * r;

        System.out.println("面积为:" + s);
    }

    public void area2(double pai){

        double s = pai * r * r;

        System.out.println("面积为:" + s);
    }


    public double area3(double r,double pai){

        double s = pai * r * r;

        return s;
    }


}

